$ 3^{-4}$
Solution: $= \left(\dfrac{1}{3}\right)^{4}$ $= \left(\dfrac{1}{3}\right)\cdot\left(\dfrac{1}{3}\right)\cdot \left(\dfrac{1}{3}\right)\cdot \left(\dfrac{1}{3}\right)$ $= \dfrac{1}{9}\cdot\left(\dfrac{1}{3}\right)\cdot \left(\dfrac{1}{3}\right)$ $= \dfrac{1}{27}\cdot\left(\dfrac{1}{3}\right)$ $= \dfrac{1}{81}$